Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted aircharge and improving peak power outputs. The boost pressure may be regulated to a desired set-point through the actions of one or more boost actuators including, for example, a wastegate (WG) coupled across an exhaust turbine and a compressor surge valve (CSV) coupled across an intake compressor. The wastegate regulates the boost pressure by controlling the exhaust gas flow over the turbine while the compressor surge valve is commonly used for compressor surge management. Each actuator may be adjusted based on feed-forward and feedback components.
As one example, wastegate adjustments affect the boost pressure through relatively slow turbocharger dynamics while CSV adjustments, as well as intake throttle adjustments, affect the boost pressure through relatively fast dynamics. Due to the different dynamics, the action of the intake throttle, may have an immediate effect on boost pressure and may confound the wastegate control loop. As a result, the engine may operate, at least temporarily, in or close to a hard or soft surge region. Leaving the CSV open (when possible without degrading engine torque delivery) may alleviate surge tendencies but may lead to elevated exhaust pressures and increased engine pumping work. In addition, fuel economy may be degraded due to extra compressor work needing to be compensated by increased turbine work.
The inventors herein have identified that some of the above issues may be addressed by a method for a boosted engine system comprising: concurrently adjusting each of a wastegate, a compressor recirculation valve (CCRV), and an intake throttle to provide a desired boost pressure and manifold air flow. In this way, by operating the CCRV actuator in coordination with the intake throttle and the wastegate, a faster and more accurate regulation of boost pressure and engine torque output is achieved.
For example, a boosted engine system may include a turbocharger having a wastegate actuator coupled across the turbine and a continuously variable compressor recirculation valve (CCRV) coupled across the compressor. The CCRV may be configured like an intake throttle so that it can be actuated fully open, fully closed, or any position there-between. In response to a boost demand, a controller may feed-forward adjust the wastegate position based on the desired (or reference) boost pressure and the operating conditions. For example, to increase boost pressure, the wastegate may be moved to a more closed position to increase turbine inlet pressure and turbine speed, while to decrease boost pressure, the wastegate may be moved to a more open position to decrease turbine inlet pressure and turbine speed. In addition, feedback adjustments to wastegate position may be based on the difference between the actual (measured) boost pressure and the desired boost pressure.
As such, due to the slow turbocharger dynamics associated with the actuation of the wastegate, the desired boost pressure change is achieved slowly since the wastegate first needs to accelerate (or decelerate) the turbine and the compressor. Thus, in coordination with the wastegate adjustment, a compressor recirculation valve (CCRV) is adjusted concurrently. Specifically, the CCRV is feed-forward adjusted based on operating conditions and a compressor pressure ratio to move turbocharger operation away from a hard surge limit to within a soft surge region. The CCRV is then feedback adjusted to correct for boost errors resulting from the wastegate adjustment. Since the impact of the CCRV adjustment on boost pressure is substantially immediate, the CCRV and the wastegate can be used together to provide accurate steady state boost pressure regulation in the presence of uncertainties and external disturbances. Likewise, intake throttle adjustments may also be concurrently used to take advantage of the rapid turbocharger dynamics associated with throttle actuation. For example, the intake throttle is adjusted based on a manifold flow rate error resulting from the wastegate and the CCRV adjustments, and in relation to the desired manifold flow rate. The throttle adjustment thereby allows for a more accurate air flow, and consequently more accurate torque delivery, in the boosted operating region.
In this way, a combination of wastegate, compressor recirculation valve, and intake throttle adjustments may be used to improve boost delivery and torque output. By using a continuously variable compressor recirculation valve to provide boost control in a frequency band that is complementary to the frequency band of the wastegate, both boost actuators may complement each other to provide higher gain tuning of boost pressure, improved boost response and more accurate boost pressure delivery while operating the compressor away from a surge limit. By also adjusting an intake throttle to correct for air flow rate errors resulting from the boost pressure control, both an accuracy and speed of torque delivery during boosted engine operation is improved. Overall, boosted engine performance is improved, providing fuel economy benefits.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.